The present invention relates to a presensitized plate for use in making a lithographic printing plate and more specifically to a presensitized plate for use in making a lithographic printing plate whose adhesion of a light-sensitive layer to a substrate is improved and which is provided with a light-sensitive layer comprising a photodimerizable polymer.
There have been well-known photocross-linkable materials which cause photocross-linking through a cyclization-addition reaction. These materials have widely been used as principal components of a light-sensitive composition which is employed for making presensitized plates for use in making lithographic printing plates (hereunder referred to as "PS plates" ) or materials for forming photoresist images. Although these photocross-linkable polymers are highly sensitive and effectively used as photoresists, they have not yet been practically used because of their poor adhesion to a substrate or other layers. Such poor adhesion possibly leads to peeling off of images, formation of defects or the like during rubbing with a brush when an imagewise exposed PS plate is developed and, therefore, sufficient printing durability cannot be imparted to the resulting lithographic printing plates. Moreover, this tendency becomes conspicuous when a PS plate is exposed to light of low intensity and as a result, its sensitivity becomes low.
There have been known a variety of methods for improving adhesion of such a photocross-linkable light-sensitive material to substrates or other layers. For instance, Japanese Patent Un-examined Publication (hereunder referred to as "J.P. KOKAI") No. Sho 62-78544 teaches the addition of a negative-working diazo resin to the light-sensitive layers of PS plates; and J.P. KOKAI No. Sho 62-85255 discloses a method for improving the adhesion by expanding pores of an anodized layer formed on an aluminum substrate to ensure a physical anchor-effect.
However, the addition of diazo resins to light-sensitive layers becomes causes of various problems. For instance, the sensitivity of the layer is lowered; and the stability of pigments (coloring agents) is impaired during storing the light-sensitive composition containing such a diazo resin in the form of a coating solution. In addition, the method for enhancing the anchor-effect of the surface of a substrate suffers from various drawbacks, for instance, the non-image areas of the resulting lithographic printing plate is liable to receive ink during printing. This inevitably leads to background contamination.